Field of the Invention
The invention relates generally to methods of directionally drilling wells, particularly wells for the production of hydrocarbon products. More specifically, it relates to a method of automatic control of a steerable drilling tool to drill wells along a planned trajectory.
Background Art
When drilling oil and gas wells for the exploration and production of hydrocarbons it is often desirable or necessary to deviate a well in a particular direction. Directional drilling is the intentional deviation of the wellbore from the path it would naturally take. In other words, directional drilling is the steering of the drill string so that it travels in a desired direction.
Directional drilling can be used for increasing the drainage of a particular well, for example, by forming deviated branch bores from a primary borehole. Directional drilling is also useful in the marine environment where a single offshore production platform can reach several hydrocarbon reservoirs by utilizing a plurality of deviated wells that can extend in any direction from the drilling platform.
Directional drilling also enables horizontal drilling through a reservoir. Horizontal drilling enables a longer section of the wellbore to traverse the payzone of a reservoir, thereby permitting increases in the production rate from the well.
A directional drilling system can also be used in vertical drilling operation. Often the drill bit will veer off of a planned drilling trajectory because of an unpredicted nature of the formations being penetrated or the varying forces that the drill bit experiences. When such a deviation occurs and is detected, a directional drilling system can be used to put the drill bit back on course with the well plan.
Known methods of directional drilling include the use of a rotary steerable system (“RSS”). The drill string is rotated from the surface, and downhole RSS causes the drill bit to drill in the desired direction. RSS is preferable to utilizing a drilling motor system where the drill pipe is held rotationally stationary while mud is pumped through the motor to turn a drill bit located at the end of the mud motor. Rotating the entire drill string greatly reduces the occurrences of the drill string getting hung up or stuck during drilling from differential wall sticking and permits continuous flow of mud and cuttings to be moved in the annulus and constantly agitated by the movement of the drill string thereby preventing accumulations of cuttings in the well bore. Rotary steerable drilling systems for drilling deviated boreholes into the earth are generally classified as either “point-the-bit” systems or “push-the-bit” systems.
When drilling such a well an operator typically referred to as a directional driller is responsible for controlling and steering the drill string, or more specifically, the bottom-hole assembly (BHA), to follow a specific well plan. Steering is achieved by adjusting certain drilling parameters, for example, the rotary speed of the drill string, the flow of drilling fluid (i.e., mud), and/or the weight on bit (WOB). The directional driller also typically operates the drilling tools at the end of the drill string so that the drilling direction is straight or follows a curve. These decisions to adjust the tool settings (e.g., the drilling parameters and/or the settings of the drilling tools) are made based on a data set that is measured at the surface and/or measured downhole and transmitted back by the downhole tools. An example of the data transmitted by the tools is the inclination and the azimuth of the well, as both are measured by appropriate sensors, referred to as D&I sensors in oilfield lexicon, in the bottom-hole assembly (BHA).
PowerDrive Archer is Schlumberger's addition to the PowerDrive line of RSS. Because all external parts of the new drilling system rotate, it is able to drill high dogleg severity wells in a single run, and at a far superior rate of penetration (ROP) than a Positive Displacement Motor (PDM). This fully rotating RSS repeatedly and consistently delivers high build rates from any inclination—in field trials more than 17°/100 ft. This revolutionary full-tool rotation greatly reduces mechanical or differential sticking, rendering a much cleaner wellbore for easier well completion and more accurate well logging. PowerDrive Archer's higher “build rate” (e.g. ability to turn faster) also enables it to “kick off” (e.g. begin turning from the vertical well section) later and enter the well's horizontal section earlier, thus increasing exposure to the reservoir's pay zone and boosting potential for hydrocarbon production.